You can add the Reference objects to your Scatter Chart.
X- and Y- Axis Reference Lines
Reference lines are vertical or horizontal lines in a graph, related with user-defined values on the x-axis and y-axis respectively. Mathematically speaking a horizontal reference line is displaying all x-values for a given y and a vertical reference line is displaying all y-values for a given x. You can add them easily in your Scatter Chart by just defining the values and labels for X- and Y-Axis reference lines.
Style each of your reference lines.
Choose the label color.
Set the font-size of the label.
Set the font Family of the label (choose one or define your own).
Decide whether you wish to make the label bold/italic/underlined.
Adds shadow effects to your label.
Choose between vertical/ horizontal orientation.
Choose the left/ center/ right position for the Label on Y-Axis reference line.
Define the color of your reference line.
Define the width (thickness) of your reference line.
Choose normal or dashed line style.
Show/Hide the reference line depending on a calculation condition.